The present invention is directed to triazine compounds, polymers comprising triazine structural units, and methods for their preparation. More particularly, the present invention is directed to triazine compounds capable of reacting with nucleophilic groups on polymers or monomers; polymers which comprise at least one triazine moiety; and methods for preparing the polymers.
Many polymers as synthesized contain nucleophilic end-groups or nucleophilic groups as pendant groups in the chain of the polymer, or both. Nucleophilic end-groups may adversely affect the properties of the polymers when the polymers are used in certain applications. For example, the presence of hydroxy end-groups in poly(arylene ether)s may result in decreased thermal stability. Similarly, the presence of hydroxy end-groups in polycarbonates may result under certain circumstances in poorer color or optical hue, high surface static charging, sticking, and dust attraction after injection molding, poorer heat and water resistance, and poorer heat aging resistance. Polymers in which nucleophilic end-groups, particularly hydroxy end-groups, have been capped may exhibit improved properties compared to the corresponding polymers which have not been endcapped.
Capping of nucleophilic groups on polymers may be employed not only to improve physical properties but also to introduce into the polymer reactive functionality different from the initial nucleophilic group. For example introduction of epoxy, orthoester, or olefinic functional groups through capping with appropriate epoxy-, orthoester-, or olefin comprising capping agents may provide reactive polymers which may be used in various applications such as copolymer formation for compatibilization of immiscible polymer blends. Capping of nucleophilic groups on polymers may also result in chain-extension or branching of the polymers if a difunctional or trifunctional capping agent is used and more than one nucleophile-terminated chain participates in reaction. Also, capping of nucleophilic groups on polymers may result in cross-linked polymers if the nucleophilic groups comprise pendant groups and a difunctional or trifunctional capping agent is used. Chain-extended, branched, and cross-linked polymers often have improved properties such as increased melt strength for use in making blow molded articles.
Polymers endcapped through reaction with reactive triazine moieties have been reported. Nucleophile-terminated polymers such as hydroxy-terminated poly(arylene ether)s or hydroxy-terminated polycarbonates have been endcapped through reaction in solution with chlorotriazines as disclosed in U.S. Pat. Nos. 4,927,894, 5,034,527, 5,115,043, 5,132,373, 5,210,191, and 5,264,496. Nucleophile-terminated polymers such as amine-terminated polysiloxanes have been endcapped through reaction in solution with chlorotriazines as disclosed in U.S. Pat. No. 5,324,796. Branching of hydroxy-terminated poly(arylene ether)s using trichlorotriazine (also known as cyanuric chloride) in a solution reaction has been disclosed by White and Loucks in ACS Symposium Series, volume 282 (Reactive Oligomers), 187 (1985). Polycarbonates containing triazine structural units in the chain and also branched polycarbonates and molding compositions made therefrom have been disclosed in U.S. Pat. Nos. 3,957,728, 3,978,159, and 4,092,243. All of these references require that the incorporation of triazine structural units be carried out in a solution reaction in the presence of a base. The subsequent recovery of polymer typically requires antisolvent precipitation and drying of recovered polymer. Methods must be provided for solvent recovery and disposal of any salt derived from the base. A method is needed which provides a polymer with capped nucleophile groups in a melt process without the need for a base or recovery of large volumes of solvent.
Melt processes for endcapping of nucleophile-terminated polymers have been reported which rely on transesterification with a reactive ester. For example in U.S. Pat. No. 5,696,222 and in European Patent Application EP 703,261 hydroxy-terminated polycarbonate is capped through transesterification with a reactive ester. In one illustrative process a bisphenol and diphenylcarbonate (DPC) are used as reactants for synthesis of a polycarbonate in a melt transesterification process. Endcapping of hydroxy end-groups to yield phenyl-capped end-groups derived from DPC may be achieved by using a stoichiometric excess of DPC to give a desired endcap level and by driving the reaction equilibrium by applying a vacuum to remove the phenol byproduct. However, either excess DPC must be used at the beginning of the reaction or additional DPC must be added at a later reaction stage to compensate for the evaporative loss of the more volatile DPC reactant during later reaction stages at higher temperatures and pressures. Such use of excess DPC can give a higher endcap level, but these off-stoichiometry conditions sacrifice reaction rate and molecular weight. In addition, late addition of DPC is limited in effectiveness because of DPC's volatility under the later reaction conditions of higher temperature and lower pressure, and the DPC lost in later reaction stages must be separated from the phenol byproduct if they are to be recycled.
Another disadvantage is that the typical synthesis of a melt polycarbonate from a bisphenol and a diarylcarbonate such as DPC offers only the possibility of having unfunctionalized aryl end-groups on the polymer unless other monophenols are added early in the reaction or unless a post-reaction process is used. Adding a monophenol can change the end-group type, but may also adversely affect reaction rate and molecular weight of the polymer. Also added monophenols may be volatile under the reaction conditions. Also endcappers in post-reaction processes are often activated carbonates having a reactive leaving group which must be prepared using the toxic chemical phosgene and thus are not readily available at low cost.
A problem to be solved is to provide capping agents which are low cost, which react with nucleophile-containing monomers or with nucleophile-containing polymers during or subsequent to their synthesis, particularly in a melt process, and which release a species from the capping agent which in one embodiment may be easily removed, such as by devolatilization, and optionally recovered. In various embodiments it is also desirable that a capping agent impart some property improvement to a polymer composition, for example through removal of residual nucleophilic groups such as hydroxy groups, or through the presence of beneficial substituents on a capping agent attached to a polymer. In another embodiment it is desirable that a capping agent be capable of modification to introduce functionality into a nucleophile-containing polymer for subsequent reaction. In still another embodiment it is desirable that a capping agent be capable of reacting with a nucleophile-containing monomer as a participating species in a polymerization reaction. In still another embodiment it is desirable that a capping agent be employable in a manner such as to allow a polymerization to be carried out rapidly at close to stoichiometric conditions until a desired molecular weight is achieved and then to rapidly increase the endcap level and/or molecular weight to a desired level by adding an endcapping agent. In still another embodiment it is desirable that a capping agent be capable of modification to provide a chain-extension, branching, or cross-linking agent. After diligent experimentation the present inventors have discovered solutions to these problems.